Best Practices From no Wordpress to Local Computer back to Wordpress

Can someone help to what is the best way and order to approach and accomplish the following:

Using a PC/Win 10 i7 8700

  1. Download or Pull an existing website hosted with another service (Not Wordpress) using Flywheel local and then placing onto a local computer to where it can be worked on? Is there another program needed in addition to Flywheel local ?

  2. Then at what point can or is the best point to apply the Wordpress template to the site that was not prepared with Wordpress.

  3. When hosing with Flywheel what do you need to do to make the server Word Press Ready ? Also how easy is to replace or try out new Templates ? Thanks Just trying to sort thinks out and what’s the best way to handle such ?